Casting method and apparatus



Oct. 7, 1958 Filed Nov. 13, 1945 C F. GRAY ETAL CASTING METHOD AND APPARATUS 2 Sheets-Sheet 1 oct. 7, 195s .F. GRAY mL 2,854,713

CASTING METHOD AND APPARATUS Filed Nov. 13, 1945 2 Sheets-Sheet 2 United States Patent O "ice CASTING Mn'rHoD AND APPARATUS C. F. Gray, Ames, and Richard H. Thompson, Cedar Application November 13, 1945, Serial No. 628,319

6 Claims. (Cl. 22-73) The present invention relates to the casting of metal into small billets of a desired shape from crude rough biscuits of reduced metal. YThe invention is particularly applicable to the casting of small billets of uranium and other heavy metals varying in size from l to 500 grams.

Heretofore, ditliculties have been encountered in casting billets of uranium and similar heavy metals withinv the weight limits just indicated. Because of the small amount of metal involved, the melt may Vnot settle in a clear pool but may remain as droplets in the llux. Castings or billets moulded from molten metal in this condition may not properly conform to the mold and, as a result, may contain irregularities. Furthermore, the metal in the castings may not be homogeneous and, therefore, may be more vulnerable to galvanic deterioration.

Another dilliculty that may be encountered in connection with the melting of small ingots of uranium and similar heavy metals arises from the iilm or skin formed by the outside layer of the ingot which continues to encase and restrain the interior metal after it has been heated to a molten condition. In order to pour the metal, the skin must be broken. Furthermore, capillary attraction and pockets formed by the pierced kskin may prevent some of the available molten metal from owing to the mold.

It is, therefore, an object of this invention to overcome these difficulties, and to provide a novel improved apparatus and method for small-scale casting of metal objects such as, for example, uranium billets.

A further object is to provide a novel small-scale casting furnace including a melt crucible and cooperating plunger that is operable to squeeze the molten metalout of an enclosing skin while the metal, flux, and:moldare under reduced pressure.

Another object is to provide a novel furnace of this type having a crucible and cooperating plunger, the crucible having a centrally disposed aperture in the bottom and a pouring rod adapted to open and close the aperture, and, in addition, to break any restraining skin or film about the molten metal.

The invention, accordingly, resides in the novel method and in the novel features of construction, combination of elements, and arrangement of parts which will be exemplied in the construction hereinafter set forth in conjunction with the drawings and the scope of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of the invention, reference may be had to the following detailed description taken in connection with the accompanying drawings, in which:

Fig. 1 is a vertical cross-sectional view of a small scale casting apparatus embodying the present invention and illustrating the plunger and pour rod in the melting position;

Fig. 2 is a sectional view taken through line 2 2 of Fig. l;

Patented Oct. 7, 195,8

Fig. 3 is a sectional viewtaken throughvline'3-3 of Fig. 1; and

Fig. 4.is: an enlarged view of a portion ofv Fig. 1 illus- Vtratingthezplungerand the. pour rod in pouring position.

Figure 5 is a still more enlarged fragmentary'sectional view of the bottom part of the crucible and the end `portion of the plunger showing, to anl exaggerated degree, the incongruity of the bottom surface of the plunger and the opposite surface of the crucible.

Referring to the drawings, the casting apparatus 'illustrated generally includes a graphite crucible 10' having a hemispherical bottom` surface 11. in which a uranium pig or biscuit B may be melted. An outlet aperture or spout 12 is normally closedwith the hemispherical end 13 of a graphite pour'rod 14. When the desired pouring temperature for thez'uranium pig B is reached, the rod 14 is raised to break any skin or film, such as an oxide skin, under or about the molten metal, after which it is lowered to open the aperture12. Associated with the crucible 10 is a graphiteiplunger 15 having a hernispherical end 16 the radius `of which is slightly larger than the radius of surface 11 as clearly shown in Fig. 5. After the molten-metal vilows out of the crucib1e10, the plunger 15 is lowered and squeezes out any metal retained in the metal skin remaining in the crucible.

The molten uranium metalifromithe `crucible 10 ows through the spout 12intoagate ori channel 17 and then into theforming hollow l'ofavgraphitemold 19 that is located beneath and supports. the crucible'lt). The crucible 10 and mold 19 are provided with interlockingends 20 so that the two members'maybe readily alignedrelative to oneanother.

The crucible and mold assemblyfis supported on-a lirebrick cylinder 21.whichxrests on a water-cooled brass base 22. Suitable inlet andioutlet connections24 .and 23 supply cooling water to the Water-jacket base'22.

A thermocouple 25 for temperature 'measurementsextends upwardly through thefbas'et22, thecylinder'ZL'and `the -mold 19 to a point inthe crucible 10 adjacent the botcentrally disposedaxial cylindrical passageway33 extend-4 ing therethrough. A steel valve rod 34 slidably supported by brace 35 extends through the passageway 33 of the base 22 and is coupled at 36 to the pour rod 14. Similarly, a push rod 37 extends through the passageway 33 of the cover 29 and is secured by a coupling 38 to a pressure rod 39 which is reciprocally guided by slideways in the top of the insulating member 26 and a crucible cover 40. The lower end of the pressure rod 39 is seated in a recess 41 in the top of the plunger 15 `so that a downward force of the rod 37 is transmitted to the plunger 15.

The assembly thus far described is made Huid-tight by suitable rubber tube vacuum seals 42 about the rods 37 and 34. In order to provide for evacuating the assembly, the cover 29 is directly sealed by one of the seals 42, Whereas the other seal 42 is secured in the lower end of a T-joint 43, the opposite end of which is tted in the passageway 33 of the base 22. The assembly may be readily evacuated to a desired sub-atmospheric pressure through opening 44 of the T-joint 43. In order to insure complete evacuation at all points in the assembly, suitable radially extending vents 45 are formed in the cylinder 21 so as to connect the passageway 33 of the base 3 22 with the interior of both the quartz Cylinder 27 and the insulator 26. Likewise, a vent 46 is disposed in the base of the crucible 10 so as to vent the mold hollow 1S to the evacuated interior of the insulator 26.

In operating the described melting-molding apparatus, the various components are assembled, as illustrated in Fig. 1, with a metal biscuit B, which in the present instance is uranium, located in the Crucible 10. The assembly then is evacuated, and thereafter the Crucible is heated as by an induction coil (not shown) around the quartz cylinder 27. When the desired pouring temperature is reached, the pouring rod 14 is raised about 1A inch to break any skin under the metal biscuit B, and then is retracted to the position illustrated in Fig. 4, After just enough time has elapsed to allow the metal to pour out of the crucible 10 into the mold hollow 1S, the plunger 15 is pushed down to squeeze out any metal retained in the metal skin or by the flux.

It will be observed that, while the crucible 10 and plunger 15 are illustrated as having hemispherical mismatched surfaces, either conical or otherwise modied surfaces may be substituted. In any case the plunger must have a Slightly larger radius for the hemispherical surface or a slightly larger angle if a conical shape is employed than the Corresponding crucible surface. This construction permits the small amount of metal retained by the skin or flux to be squeezed toward the center or pour hole.

Since certain further changes may be made in the above construction and different embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense, the invention being dened by the appended claims.

What is claimed is:

l. The method of casting into a billet a metal pig having a retaining skin when in a molten state, which comprises the steps: melting the metal within a vacuum, piercing the skin at the bottom of said pig while maintaining a vacuum whereby the molten metal flows down from said skin, and squeezing the skin around the molten metal thereby causing a small amount of metal retained by the skin to be separated therefrom.

2. The method of casting into a billet a uranium biscuit having a retaining oxide skin when in a molten state comprising the steps of melting the metal in a vacuum, piercing said skin at the bottom, allowing the main prtion of the molten uranium to separate from the skin by gravity, and squeezing the skin to remove a small amount of metal still retained by the skin.

3. In combination, apparatus for melting and casting uranium pigs having an oxide skin in vacuo, comprising a chamber construction, means for evacuating the chamber, means for melting uranium disposed in the chamber, means for casting the molten uranium into a billet mounted within the chamber and in position to receive melting uranium whereby the molten uranium may discharge into the means for casting the molten uranium into a billet, means adapted for upwardly piercing the skin at the bottom of the molten uranium thereby discharging the molten uranium into the aforesaid means for casting the molten uranium, and means for subsequently squeezing the skin of the molten uranium downwardly whereby any of the molten uranium retained by the skin is forced into the aforesaid means for casting the molten uranium into the billet.

4. In combination, a Crucible provided with a bottom of steadily diminishing cross-section and having an outlet opening centrally arranged in said bottom, and a plunger contacting the side walls of said crucible and having a contact portion of diminishing cross-section eX- tending into the crucible toward the bottom thereof, said plunger contact portion having the corresponding radii of the diminishing cross-section greater than those of the Crucible bottom.

5. ln combination, a crucible having a concave bottom surface of substantially hemispherical shape, and having an outlet opening centrally arranged in said bottom, and a plunger in the crucible contacting the side walls of said crucible and having a convex contact portion of substantially hemispherical shape, the radius of curvature of contact portion of the plunger being greater than the radius of curvature of the bottom surface of the crucible.

6. An apparatus for producing castings of pure uranium from a uranium mass surrounded by an oxide skin, comprising a crucible for melting said uranium, a mold for receiving the melted uranium connected with said crucible, means for evacuating said crucible and said mold, a piercing means extending upwardly into the bottom of said crucible to puncture the bottom of said oxide skin, and a downwardly-acting forcing means for pressing the melted metal out of the skin.

References Cited in the tile of this patent UNITED STATES PATENTS 477,231 Smith et al. June 2l, 1892 1,022,910 Whitney Apr. 9, 1912 1,521,526 Godai Dec. 30, 1924 1,540,515 Cuenot June 2, 1925 1,542,598 Begtrup June 16, 1925 1,542,784 Deppeler June 16, 1925 1,568,685 Moore Jan. 5, 1926 

1. THE METHOD OF CASTING INTO A BILLET A METAL PIG HAVING A RETAINING SKIN WHEN IN A MOLTEN STATE, WHICH COMPRISES THE STEPS: MELTING THE METAL WITHIN A VACUUM, PIERCING THE SKIN AT THE BOTTOM OF SAID PIG WHILE MAINTAINING A VACUUM WHEREBY THE MOLTEN METAL FLOWS DOWN 